Optimization of indigestible neutral and acid detergent fiber measurement protocols*

The objective was to evaluate the effect of using a diet predigestion (PD) of HCl and pepsin along with different in situ ruminal incubation lengths on indi- gestible NDF (INDF) and ADF (IADF) content recovery from diet and fecal samples. Diet and total fecal collec- tion samples from steers fed a high-roughage starter or a low-roughage finisher diet were collected from a larger experiment. Diet samples either underwent PD or not (NPD). Then, diet and fecal samples were ruminally in- cubated for 72, 96, 120, or 288-h. After incubation, NDF or ADF protocols were conducted to determine INDF and IADF. For PD, a 120-h ruminal incubation length was needed to achieve fecal recoveries that were not different from 100% for all marker by diet combinations. For NPD, a 288-h incubation was required to achieve 100% fecal recovery for all diet by marker com- binations, except for IADF with the finisher diet. A 120-h incubation resulted in the highest agreement Lin's concor- dance correlation coefficient (CCC) ≥0.90 with observed dry matter digestibility (DMD) for INDF and IADF for PD. With NPD, a 288-h incubation was needed to achieve estimates of DMD with excellent agreement (CCC ≥0.89) for INDF and IADF. Based on these re- sults, PD followed by a 120-h ruminal incubation shortens time requirements and provides acceptable measurements of INDF and IADF concentrations in feeds and feces. For NPD a 288-h ruminal incubation length is required.